The present invention relates to riveting apparatus and methods. More particularly, the invention relates to improved anvil devices and novel riveting methods including replacement of disposable anvil heads.
It is known to provide elongate rigid anvils for setting tubular or semi-tubular rivets. The anvils are composed of an elongate hollow cylinder, one end of which is retained in the riveting machine and the other having a rivet clinching or clenching surface. Typically, a pilot pin or roll pin is located within the cylinder, the end of the pin being extendable through the clinching surface. The pin is spring-loaded to extend from the clinching surface an amount limited by a shoulder on the pin contacting a shoulder within the cylinder.
Tubular or semi-tubular rivets include a relatively large diameter head portion and a reduced diameter tubular or cylindrical portion which is hollow along at least a portion of its longitudinal length to form a rivet bore. The diameter of the rivet bore varies in accordance with rivet size, and a correspondingly sized anvil having a suitably sized pin and clinching surface is required to set or clinch the rivet. For example, truck brake shoe linings are typically assembled with 1/4" or 3/16" diameter rivet by various manufacturers. The anvils are elongate to allow the anvil to reach into irregular shaped work pieces such as brake shoes.
The anvil is mounted in a mechanically, pneumatically or hydraulically operated riveting machine for closing movement with a driver head arranged to engage the remote side of the rivet head. The work pieces to be joined are positioned between the anvil and the driver head. The anvil pilot pin extends through a riveting hole in the work pieces to be joined and into the bore the tubular or semi-tubular rivet. As the head of the rivet is driven towards the anvil, the pilot pin guides the rivet through the work piece, retracting as it goes.
As the end of the pilot pin nears the clinching surface, the pin bottoms out and the wall of the rivet starts expanding by being forced over the now stationary pin.
When the wall of the rivet contacts the clinching surface it is rolled radially outward and then back against the work piece. This clinching surface is made up of a cupped annular rivet rolling surface located about the pilot pin. After removal of the work piece, the spring loaded pilot pin again extends in preparation for the next rivet.
The annular rivet rolling surface is critical to the proper clinching of the rivets. To insure proper clinching, the rivet rolling surface is highly polished. If it becomes damaged or worn, rivets may split or fail to clinch properly. This lessens the strength and durability of the riveted connection between the parts and, in some cases, causes failure to meet product specifications. In the latter case, the part must be returned to the manufacturing line for removal of the defective rivet and, in some instances, all other simultaneously made rivet connections, so that the part may be processed once again in the riveting machine. All such corrective processing is costly.
Not only does the rolling surface wear, but many times a piece of foreign matter will damage the rolling surface of a nearly new anvil. In either case, heretofore, the entire anvil had to be replaced.
Heretofore, the anvil cylindrical portion and clinching head were integrally formed to assure stability of the elongate anvil tool and alignment of the pilot pin within the anvil bore and the rivet during the life of the anvil. Such integral or one piece construction was believed necessary to a satisfactory anvil life wherein high riveting loads are intermittently applied and work pieces are aligned for each rivet cycle.